Absolute encoder and absolute value signal generation method

ABSTRACT

An absolute encoder comprising a first memory operable to store a first absolute value signal produced every constant time period, the absolute value signal representing an absolute value position. A second memory stores a second absolute value signal produced in a previous time period. A comparing/calculating section compares the first absolute value and the second absolute value and produce a difference amount. A dividing process section divides the difference amount in an equal rate within a producing time period of said first absolute value signal. An interpolated absolute value signal producing section reads the second absolute value signal and adds the difference amount in a stepwise manner.

TECHNICAL FIELD

The present invention is related to a vernier type absolute encoder andan absolute value signal producing process method thereof, which arecapable of producing a continuous interpolated absolute value signalfrom an absolute value signal which is intermittently produced in aconstant time period, while the interpolated absolute value signal doesnot depend upon an absolute value producing time period, a control timeperiod of a motor control apparatus, and a transfer method. Also, acorrect motor feedback rotation angle can be obtained, and furthermore,even when erroneous operation occurs due to noise and the like, errorscannot be stored in the vernier absolute encoder and the absolute valuesignal producing process method.

BACKGROUND ART

Conventionally, an absolute encoder capable of producing an absolutevalue signal in a constant time period is constructed as shown in FIG.4. It should be understood that both the conventional technique and thepresent invention will be explained by exemplifying vernier typeabsolute encoders.

FIG. 4 is a block diagram for schematically indicating a signalprocessing section of the conventional vernier type absolute encoder. InFIG. 4, reference numeral 1 shows a rotary disk; reference numeral 2indicates a slit stream; reference numeral 3 represents a magneticsensor; reference numeral 4 denotes a phase modulating section;reference numeral 5 shows a phase difference signal producing section;reference numeral 6 indicates an absolute value signal producingsection; reference numeral 7 represents an oscillator; reference numeral8 denotes a reference signal producing section; reference numeral 9indicates a modulation signal producing section; reference numeral 20shows a data transfer section; reference numeral 21 is a motor; andalso, reference numeral 22 represents a motor control apparatus.

While positional information of the same equal pitch is formed on therotary disk 1, 4 sets of the slit streams 2 are provided, the pitchnumbers of which are different from each other. The magnetic sensor 3 isconstituted by an MR element and a bias magnet, and outputs two phasesof sine waves having pitches equal to the slit pitches. The sine wavesignals outputted from the magnetic sensor 3 are inputted to the phasemodulating section 4 so as to be converted into phase signals φ1, φ2,φ3. The respective phase signals φ1, φ2, φ3 are entered to the phasedifference signal producing section 5. The phase difference signalproducing section 5 detects phase differences between φ1, φ2, φ3 and φ0so as to produce phase difference signals (φ0−φ1), (φ0−φ2), (φ0−φ3).These phase difference signals (φ0−φ1), (φ0−φ2), (φ0−φ3) are entered tothe absolute value signal producing section 6, so that the absolutesignal producing section 6 intermittently, produces an absolute valuesignal “p” in the time period of the phase signal φ0. Also, since thisproduced absolute value signal “p” is used so as to control the motor 21on which the rotary disk 1 is mounted, this absolute value signal “p” istransferred in either a parallel mode or a serial mode by the datatransferring section 20 to the motor control apparatus 22 (for instance,republished Japanese Patent No. WO/05553).

However, the conventional technique owns the below-mentioned problems.

FIG. 5 is a diagram for showing a relationship as to motor feedbackrotation angles, namely, FIG. 5( a) indicates such a motor feedbackrotation angle relationship in the case that a motor control time periodand an absolute value producing time period are defined in a synchronousmanner, and FIG. 5( b) shows such a motor feedback rotation anglerelationship in the case that a motor control time period and anabsolute value producing time period are defined in an asynchronousmanner.

(1). In the case that the motor 21 which should be controlled is rotatedat a constant speed by using the intermittently produced absolute valuesignal “p”, if the motor control time period of the motor controlapparatus 22 is synchronized with the absolute value producing timeperiod, then such a motor feedback rotation angle having no speedvariation can be obtained as represented in FIG. 5( a). In order tosynchronize the motor control time period with the absolute valueproducing time period, timing on the side of the motor control apparatus22 must be matched with timing on the side of the encoder. Also, in sucha case that the absolute value producing time period is changed due tochanges in technical specifications of the rotary disk 1 and the slitstream 2, technical specifications of the motor control apparatus 22 arealso required to be changed.

(2). Also, when the motor control time period is not synchronized withthe absolute value producing time period, as represented in FIG. 5( b),the motor feedback rotation angle acquired by the motor controlapparatus 22 becomes such a signal having a speed variation, and thus,the encoder can hardly acquire the continuous interpolated absolutevalue signal.

(3). Also, there is another producing method. That is, an absolute valueis read when an initial setting operation is carried out, andthereafter, an incremental signal is produced so as to increment aninitial absolute signal. However, in such a case that an erroneousoperation occurs due to noise, or the like, there is a problem thaterrors are stored and an absolute position is shifted.

The present invention has been made to solve the above-describedproblem, and therefore, has an object to provide both an absoluteencoder and an absolute value signal producing process method of theabsolute encoder, which are capable of producing a continuousinterpolated absolute value signal from an absolute value signal whichis intermittently produced in a constant time period, while theinterpolated absolute value signal does not depend upon an absolutevalue producing time period, a control time period of a motor controlapparatus, and a transfer method.

DISCLOSURE OF THE INVENTION

To solve the above-described problem, the present invention recited inClaim 1 is related to an absolute encoder. That is, in such an absoluteencoder comprising: a plurality of slit streams having different pitchnumbers from each other, in which positional information of the samepitch is formed; a plurality of sensors which are relatively moved withrespect to the slit streams so as to detect the positional information;a phase modulating section for converting a signal derived from thesensor into a phase signal; a phase difference signal producing sectionfor converting both the phase modulation signal and a phase differencesignal between two pieces of arbitrary phase signals into a digitalsignal; and an absolute value signal producing section for producing asignal which is related to an absolute value position in a constant timeperiod based upon the digital signal converted by the phase differencesignal producing section and the phase difference signal, the absoluteencoder is arranged by: a first memory for storing thereinto an absolutevalue signal which is produced by the absolute value signal producingsection every constant time period; a second memory for storingthereinto an absolute value signal which has been produced inone-preceding time period with respect to a time period of an absolutevalue signal entered into the first memory; a comparing/calculatingsection for comparing the absolute value signal stored in the firstmemory with the absolute value signal which has been produced in theone-preceding time period and has been stored in the second memory so asto calculate an increase/decrease amount; a dividing process section fordividing the increase/decrease amount in an equal rate within aproducing time period of the absolute value signal; and an interpolatedabsolute value signal producing section for reading the absolute valuesignal which has been produced in the one-preceding time period, andthereafter, for adding/subtracting the divided increase/decrease amountin a stepwise manner with respect to the read absolute value signal.

Also, the present invention recited in Claim 2 is related to an absolutevalue signal producing process method of an absolute encoder. That is,in such an absolute encoder in which: positional information as to aplurality of slit streams having different pitch numbers from each otheris detected by a plurality of sensors; a signal derived from the sensoris converted into a phase signal by a phase modulating section; both thephase modulation signal and a phase difference signal between two piecesof arbitrary phase signals are converted into a digital signal by aphase difference signal producing section; and a signal related to anabsolute value signal is produced in a constant time period based uponthe digital signal converted by the phase difference signal producingsection and the phase difference signal by an absolute value signalproducing section, an absolute value signal producing process method ofthe absolute encoder is featured by that an absolute value signal whichis produced by the absolute value signal producing section everyconstant time period is stored into a first memory; an absolute valuesignal which has been produced in one-preceding time period with respectto a time period of an absolute value signal entered into the firstmemory is stored into a second memory; the absolute value signal storedin the first memory is compared with the absolute value signal which hasbeen produced in the one-preceding time period and has been stored inthe first memory by a comparing/calculating section so as to calculatean increase/decrease amount; the increase/decrease amount is divided bya dividing process section in an equal rate within a producing timeperiod of the absolute value signal; and after reading the absolutevalue signal which has been produced in the one-preceding time period,the divided increase/decrease amount is added/subtracted in a stepwisemanner with respect to the read absolute value signal by an interpolatedabsolute value signal producing section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a signal processing section of a verniertype absolute encoder for indicating an embodiment of the presentinvention.

FIG. 2 is a structural diagram of a dividing process section for showingthe embodiment of the present invention.

FIG. 3 is a relationship diagram of a motor feedback rotation angle forindicating the embodiment of the present invention.

FIG. 4 is the block diagram of the signal processing section of theconventional vernier type absolute encoder.

FIG. 5 is the relationship diagram of the motor feedback rotation angle,i.e., FIG. 5( a) shows the motor feedback rotation angle relationship inthe case that the motor control time period is synchronized with theabsolute value producing time period, and FIG. 5( b) shows the motorfeedback rotation angle relationship in the case that the motor controltime period is not synchronized with the absolute value producing timeperiod.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to drawings, an embodiment of the present invention willbe described.

FIG. 1 is a block diagram for schematically indicating a signalprocessing section of a vernier type absolute encoder which representsan embodiment of the present invention. FIG. 2 is a structural exampleof a dividing process section which indicates the embodiment of thepresent invention. FIG. 3 is a relationship diagram of a motor feedbackrotation angle which shows the embodiment of the present invention. Itshould be understood that when structural elements of the presentinvention are the same as those of the conventional technique,explanations thereof are omitted, and only different points will beexplained.

In FIG. 1, reference numeral 23 shows a first memory; reference numeral24 indicates a second memory; reference numeral 25 represents acomparing/calculating section; reference numeral 26 denotes a dividingprocess section; and reference numeral 27 shows an interpolated absolutevalue signal producing section.

In other words, the vernier type absolute encoder, according to thepresent invention, is featured to be arranged by the first memory 23,the second memory 24, the comparing/calculating section 25, the dividingprocess section 26, and the interpolated absolute value signal producingsection 27. The first memory 23 stores thereinto an absolute valuesignal which is produced by the absolute value signal producing section6 every time a constant time period has passed. The second memory 24stores thereinto such an absolute value signal which has been producedin a time period before the time period of the absolute value signalinputted in the first memory 23 by one time period. Thecomparing/calculating section 25 compares the absolute value signalstored in the first memory 23 with the absolute value signal stored inthe second memory 24, which has been produced in one-preceding timeperiod with respect to that of the first-mentioned absolute valuesignal, and then, calculates an increase/decrease amount. The dividingprocess section 26 divides the increase/decrease amount in an equal rateduring the producing time periods of the absolute value signals. Theinterpolated absolute value signal producing section 27 reads theabsolute value signal produced in one-preceding time period, andthereafter, adds/subtracts the divided increase/decrease amounts in astepwise manner.

Next, operations of the absolute encoder will now be described.

A sensor signal outputted from the magnetic sensor 3 is entered to thephase modulating section 4 so as to be converted into phase signals “φ1”to “φ3.” In this case, a phase signal corresponds to a binary signalhaving a constant time period under such a stationary state that amodulation signal “z” is modulated by a sensor output, and an edgeposition of this phase signal with respect to a reference signal “φ”constitutes phase information. The respective phase signals “φ1” to “φ3”are inputted to the phase difference signal processing section 5. Thephase signal “φ0” derived from a slit “2−a0” becomes such a phasedifference signal (φ−φ1) by detecting a phase difference between thereference signal φ and the own phase signal φ0 in a phase differencesignal producing section 5-0. The phase signals “φ1”, “φ2”, “φ3” derivedfrom slits “2−a1”, “2−a2”, “2−a3” become such a phase difference signal(φ0−φ1), another phase difference signal (φ0−φ2), and another phasedifference signal (φ0−φ3), respectively, by detecting phase differenceswith respect to the reference signal “φ0” by the phase difference signalproducing section 5.

Signals outputted from the phase difference signal producing section 5correspond to such signals which have been converted into digitalamounts based upon a clock number of the oscillator 7 which is enteredbetween edges of two phase signals inputted to this phase differencesignal producing section 5. These signals are entered to the absolutesignal producing section 6 so as to produce an absolute value signal“p.”

The absolute value signal “p” is produced by the absolute value signalproducing section 6 every time a constant producing time period haspassed. When an absolute value signal “p(n)” is produced, this absolutevalue signal “p(n)” is stored in the first memory 23, and at the sametime, another absolute value signal “p(n−1)” which has been produced inone-preceding time period with respect to the time period of theabove-described absolute value signal p(n)” is stored in the secondmemory 24.

The comparing/calculating section 25 compares the absolute value signalp(n) which has been stored in the first memory 23 with the absolutevalue signal p(n−1) which has been stored in the second memory 24 so asto calculate an increase/decrease amount A(n−1).

The increase/decrease amount A(n−1) is entered to the dividing processsection 26, and then, this dividing process section 26 outputs such asignal that the increase/decrease amount A(n−1) has been divided in anequal rate within a producing time period.

A concrete structural example as to the above-explained dividing processsection 26 is indicated in FIG. 2. As shown in this concrete structuralexample, while a bit number which is required for a maximumincrease/decrease amount is previously calculated which may be obtainedfrom both an absolute value producing time period and a maximum rotationnumber of a motor, a binary rate multiplier circuit is employed whichcorresponds to this calculated bit number. The increase/decrease amountis set as a binary rate every absolute value producing time period, anda multicated clock is used as a clock input, so that increase/decreasepulses which have been divided in the equal rate within the producingtime period are outputted from the dividing process section 26. Themultiplicated clock is obtained by multiplicating the absolute valueproducing time period and is required for the maximum increase/decreaseamount.

The interpolated absolute signal producing section 27 reads the absolutevalue signal p(n−1) which has been produced in one-preceding time periodand has been stored in the second memory 24, and then, adds/subtractssuch increase/decrease pulses with respect to the absolute value signalp(n−1) so as to produce an interpolated absolute signal, while using theabove-described increase/decrease pulses which have been divided in theequal rate within such a producing time period corresponding to theincrease/decrease amount A(n−1) outputted from the dividing processsection 26.

The interpolated absolute value signal produced from the interpolatedabsolute value signal producing section 27 is fed back via the datatransferring section 20 to the motor control apparatus 22, and thus,this motor control apparatus 22 controls the motor 21 based upon thisdata. As a consequence, the absolute value signal “p” which isintermittently produced every producing time period can be interpolatedto produce such a continuous absolute value signal as shown in FIG. 3.

As a consequence, the absolute encoder of the present invention isarranged by such an absolute encoder comprising: a plurality of slitstreams 2 having different pitch numbers from each other, in whichpositional information of the same pitch is formed; a plurality ofsensors 3 which are relatively moved with respect to the slit streams 2so as to detect the positional information; a phase modulating section 4for converting a signal derived from the sensor 3 into a phase signal; aphase difference signal producing section 5 for converting both thephase modulation signal and a phase difference signal between two piecesof arbitrary phase signals into a digital signal; and an absolute valuesignal producing section 6 for producing a signal which is related to anabsolute value position in a constant time period based upon the digitalsignal converted by said phase difference signal producing section 5 andthe phase difference signal; in which the absolute encoder is arrangedby: a first memory 23 for storing thereinto an absolute value signalwhich is produced by the absolute value signal producing section 6 everyconstant time period; a second memory 24 for storing thereinto anabsolute value signal which has been produced in one-preceding timeperiod with respect to a time period of an absolute value signal enteredinto the first memory 23; a comparing/calculating section 25 forcomparing the absolute value signal stored in the first memory 23 withthe absolute value signal which has been produced in the one-precedingtime period and has been stored in the second memory 24 so as tocalculate an increase/decrease amount; a dividing process section 26 fordividing the increase/decrease amount in an equal rate within aproducing time period of the absolute value signal; and an interpolatedabsolute value signal producing section 27 for reading the absolutevalue signal which has been produced in the one-preceding time period,and thereafter, for adding/subtracting the divided increase/decreaseamount in a stepwise manner with respect to the read absolute valuesignal. Accordingly, the continuous interpolated absolute value signalcan be produced from the absolute value signals which are intermittentlyproduced in the constant time period, while the continuous interpolatedabsolute value does not depend upon the absolute value producing timeperiod, the control time period of the motor control apparatus 22, andthe transfer method.

Also, while the motor control period of the motor control apparatus 22need not be synchronized with the absolute value producing time period,the correct motor feedback rotation angle is obtained. Even in such acase that the absolute value producing time period is changed since thetechnical specifications as to the rotary disk 1 and the slit stream 2are changed, the technical specification with respect to the motorcontrol apparatus 2 need not be changed, and only changing of theencoder processing section can accept the above-explained specificationchanges in the rotary disk 1 and the slit stream 2.

Furthermore, as compared with such a method that the absolute value isread during the initial setting operation, and thereafter, theincremental signal is produced, and the initial absolute value signal isincremented in order to read/interpolate the absolute value signal “p”every producing time period, which is intermittently produced everyproducing time period, there is such an effect that the vernier typeabsolute encoder can be realized in which even when the erroneousoperation happens to occur due to noise, the errors are not stored.

It should also be noted that this embodiment has described such anexample that the absolute encoder is applied to the rotary type motor.However, the present invention is not limited only to this embodiment,but may be applied to a linear motor.

Also, with respect to the sensor for detecting the positionalinformation of the slit stream, the magnetic type sensor has beenexplained in the above-described example. The magnetic sensor may bealternatively replaced by an optical type sensor, or another sensorconstituted by combining a magnetic type sensor with an optical typesensor.

INDUSTRIAL APPLICABILITY

As previously described, both the absolute encoder and the absolutevalue signal producing process method thereof, according to the presentinvention, are usefully employed in, for instance, a vernier typeabsolute encoder which produces an absolute value signal in a constanttime period.

The invention claimed is:
 1. An absolute encoder comprising: a plurality of slit streams having different pitch numbers from each other, in which positional information of the same pitch is formed; a plurality of sensors which are relatively moved with respect to said slit streams so as to detect said positional information; a phase modulating section for converting a signal derived from said sensor into a phase signal; a phase difference signal producing section for converting both said phase modulation signal and a phase difference signal between two pieces of arbitrary phase signals into a digital signal; and an absolute value signal producing section for producing a signal which is related to an absolute value position in a constant time period based upon the digital signal converted by said phase difference signal producing section and the phase difference signal; wherein: the absolute encoder is arranged by: a first memory for storing thereinto an absolute value signal which is produced by said absolute value signal producing section every constant time period; a second memory for storing thereinto an absolute value signal which has been produced in one-preceding time period with respect to a time period of an absolute value signal entered into said first memory; a comparing/calculating section for comparing the absolute value signal stored in said first memory with the absolute value signal which has been produced in said one-preceding time period and has been stored in said second memory so as to calculate an increase/decrease amount; a dividing process section for dividing said increase/decrease amount in an equal rate within a producing time period of said absolute value signal; and an interpolated absolute value signal producing section for reading the absolute value signal which has been produced in said one-preceding time period, and thereafter, for adding/subtracting said divided increase/decrease amount in a stepwise manner with respect to the read absolute value signal wherein the absolute encoder is operable to provide the result of adding/subtracting as a position information.
 2. In an absolute encoder in which: positional information as to a plurality of slit streams having different pitch numbers from each other is detected by a plurality of sensors; a signal derived from said sensor is converted into a phase signal by a phase modulating section; both said phase modulation signal and a phase difference signal between two pieces of arbitrary phase signals are converted into a digital signal by a phase difference signal producing section; and a signal related to an absolute value signal is produced in a constant time period based upon the digital signal converted by said phase difference signal producing section and the phase difference signal by an absolute value signal producing section, an absolute value signal producing process method of the absolute encoder wherein: an absolute value signal which is produced by said absolute value signal producing section every constant time period is stored into a first memory; an absolute value signal which has been produced in one-preceding time period with respect to a time period of an absolute value signal entered into said first memory is stored into a second memory; the absolute value signal stored in said first memory is compared with the absolute value signal which has been produced in said one-preceding time period and has been stored in said second memory by a comparing/calculating section so as to calculate an increase/decrease amount; said increase/decrease amount is divided by a dividing process section in an equal rate within a producing time period of said absolute value signal; and after reading the absolute value signal which has been produced in said one-preceding time period, said divided increase/decrease amount is added/subtracted in a stepwise maimer with respect to the read absolute value signal by an interpolated absolute value signal producing section and providing a result of the addition/subtraction as a position information.
 3. An absolute encoder comprising: a first memory operable to store a first absolute value signal produced every constant time period, the absolute value signal representing an absolute value position; a second memory operable to store a second absolute value signal produced in a previous time period; a comparing/calculating section operable to compare the first absolute value and the second absolute value and produce a difference amount; a dividing process section operable to divide the difference amount in an equal rate within a producing time period of said first absolute value signal; an interpolated absolute value signal producing section operable to add the difference amount in a stepwise manner to the second absolute value signal wherein the absolute encoder is operable to provide the result of adding/subtracting as a position information.
 4. A position producing method comprising: storing a first absolute value signal in a first memory at every constant time period; storing a second absolute value signal produced in one-preceding time period with respect to the first absolute value signal into a second memory; calculating a difference amount between the first absolute value signal and the second absolute value signal; dividing the difference amount in an equal rate within a producing time period; and adding the difference amount in a step-wise manner to the second absolute value signal and providing a result of the addition as a position information. 